<div class="sidebar">
<ul>

<li>
<h2>Advertisement</h2>
<div class="center">
<a href="#"><img src="<?php bloginfo('template_directory'); ?>/images/ad.jpg" alt="" title="" /></a>
</div>
</li>

<?php if ( !function_exists('dynamic_sidebar') || !dynamic_sidebar(2) ) : ?>

<?php endif; ?>

</ul>
</div>